A power-open latch for a motor vehicle is known from parallel U.S. Pat. No. 6,577,911 and EP 1,225,290 which has a housing, a fork pivotal on the housing between a bolt-retaining closed position and a bolt-releasing open position, and a pawl pivotal on the housing between a blocking position engaging the fork and retaining it in the latched position and a freeing position allowing the fork to move into the unlatched position. A wheel rotatable about an axis has a radially directed cam surface on which rides a projection on the pawl. A drive motor can rotate the wheel and thereby engage its surface with the projection to displace the pawl into its freeing position. A spring is braced between the pawl and the housing and urges the pawl into the blocking position and the projection into engagement with the surface. Furthermore the wheel has a groove having a pair of ends, one radially directed flank formed by the cam surface, and an opposite radially directed flank forming another surface. The cam surface is formed as a spiral generally centered on the wheel axis and the other surface is generally centered on the wheel axis. The groove has a wide end and a narrow end.
The motor can rotate the wheel from a starting position with the pawl projection bearing on the low or radially inner end of its surface to an ending position with the pawl projection bearing on the high end of the wheel surface and hence in its freeing position to open the latch. When the motor is shut down in this ending position, a powerful torque spring reverse rotates the wheel back to the starting position allows the latch to close.
While this construction is fairly effective, has some problems. First of all the mechanism is somewhat complex. The return spring must be very strong to reverse-drive the motor. Furthermore with time the mechanism gets stiff so that the torque of the spring is not enough to reset the lock, or at least takes quite some time.